The present invention relates generally to the field of process control instruments. More particularly, the present invention relates to systems and methods for facilitating serial communication within a process control instrument.
Transmitters in the process control industry typically communicate with a controller over a two-wire circuit or control loop. The transmitter receives commands from a controller over the two-wire control loop and sends output signals representative of a sensed physical parameter back to the controller. The transmitter itself can include a number of devices such as microprocessors, memory devices, analog-to-digital convertors, digital-to-analog convertors, digital signal processors (DSPs), sensors, and other peripheral devices. Communication between the various devices inside of the transmitter typically takes place on a data bus which includes a clock line and a number of data lines. Because of concerns about current consumption and complexity, it is important to minimize the number of data bus lines required for communication between the various devices.
In many process control instruments, the sensor of the process control instrument must be electrically isolated from measurement circuitry or other devices in the process control instrument for safety purposes. An isolation barrier is used to electrically isolate the sensor from the rest of the circuitry within the transmitter. The sensor receives power and communicates with the measurement circuitry through the barrier. The barrier prevents harmful electrical discharges, sometimes present on the process control loop, from entering the measurement circuitry. While necessary for safety or other purposes, inclusion of the isolation barrier reduces the number of electrical connections allowed between the sensor and the other devices for communication, clock information and power. Conventional serial communications techniques used to transmit data across the isolation barrier frequently result in undesirably high levels of power consumption and/or complex circuitry.